The overall goals of this project are to identify consistent patterns of variance in brain function in patients at risk for Alzheimer's Disease by using APOE ε4 as a marker for disease risk. The activation Blood Oxygen Level Dependency (BOLD) signal will be compared to both resting and activation perfusion signals to assess the variability of cerebral blood flow as it relates to the BOLD signal. Each participant will be imaged on a 3T MRI scanner while performing an associate episodic memory task.